1. Field of the Invention
An automatic vehicle starter is typically used so that an operator can start a vehicle by a transmitter and without actually being inside the vehicle. In a typical automatic vehicle starter, an operator can simply push a button on a miniature transmitter to start up a vehicle. This is most often done in cold climates so that one can remotely start an automobile from inside one's home, so that the automobile is pre-heated and ready to drive away 5 or 10 minutes after it is remotely started.
2. Discussion of the Background
Conventional remote vehicle starters typically use some kind of tachometer sensing system to detect the rpms at which the engine is running, to determine how long to crank a starter motor during starting so as to crank the starter motor for a long enough period of time to start the engine. However, such systems must also try to avoid overcranking the starter motor. Typically, a remote starter should crank a starter motor until the rpms get above 400-600, at which time power to the starter motor is released but power to the ignition circuit is still applied. There are a variety of known ways to determine this tachometer input. One typical way is to place a tachometer sensor wire at the negative "-" side of the ignition coil or to place an inductive pickup sensor around one of the spark-plug wires. This will typically provide the tachometer information. This same tachometer information is also used to determine whether the car is still running. It is important to determine whether a car is still running so that everything can be turned off if the engine stalls while being remotely started.
However, such conventional remote vehicle starters suffer from significant drawbacks. First, there is a difficulty in that in some vehicles the tachometer pickup points and even spark plug wires altogether are not readily accessible or may not be accessible at all. In such systems it may not be possible to use a remote vehicle starter, or it may be very difficult to accurately get a tachometer determination. Furthermore, in diesel vehicles there are no tachometer pickup points, so that conventional remote vehicle starters cannot be used at all in diesel vehicles.